How do you beat divine intervention

Go at settings and put infinate lives and start with all guns and start with the rifle for the first 3 levels and then use the machine gun and when youre at the level 3 there's going to be a zombie hiding in the trash can so you have to duck and then use the shotgun for levels 4 and 5. when you reach the boss you just keep on shooting him at the head with a shot gun. you have to jump when he throws up a maggot and when he flies you have to duck and you also have to duck when he breathes out fire.. hope that helps you